You do not need a permission from JMIR Publications to use any part of an article published in JMIR journals, including figures, Multimedia Appendices, etc. unless the figure/Multimedia Appendix specifically states a different copyright holder than the authors, or a different license than the standard JMIR licence cc-by (see below).
All JMIR journals are open access. JMIR articles are published under a Creative Commons Attribution (cc-by) license (see copyright statement on each article), meaning that authors retain copyright but license it to anybody under the rules of the Creative Commons Attribution attribution license, which means you can use it in whatever way you like as long as
- you cite the original source (complete citation of the JMIR article with URL) and
- state that it was published (and can be reproduced) under the terms of Creative Commons Attribution 4.0 licence (or 2.0 prior to mid-May 2017).
- Creative Commons Attribution 4.0 (link to the external CC site)
- Can you give me permission to publish my article as part of my thesis?